build: Fix some GCC5.1 warnings

Not all warnings have been enabled, only the most
useful ones. This fix some outstanding issues and
try to mute most deprecated warnings in dependencies
headers.

* Add missing "defined()" macro function
* Undefine an improper macro
* Disable warnings for legacy code include
* Add missing cases for enum classes based switch
* Add a warning for potentially dangerous code
* Change ICE "onRecv()" prototype to return void
* Fix an apparently accidental virtual override signature problem
* Change a std::basic_string constructor to avoid ambiguity

Refs #74147

Change-Id: I1361fc5d16c63fd7590f8d68ffdb0e2588a8b635